yes
You can use a world editing program like MCedit.
There are single player mods that enable this as a command. But most are for multiplayer if you are searching the plugin: WorldEdit is the most chosen
No
No, you can't open the chat box, so you can't talk on single player. Edit: You can open the chatbox and use commands in the later versions of minecraft, if you select cheats enabled when creating a new world.
if you want items in minecraft the best edit i know is INVedit. download it, open world iventory and edit it. save it to your world next
by going to the minecraft website and clicking on profile, edit character, then download the skin maker
he can
Yes Just go on your server folder look for world (random name) then transfer to .minecraft/worlds launch minecraft you will find the world somewhere in singleplayer zone Select the world run it and you are where you where before. And you can still edit blocks
You can. Just get it from the Minecraft Forum. Run it, then you can make and edit skin files for Minecraft.
The only way to edit some stuff on the server is to open the server.properties in the main Minecraft folder (or server folder if you made one) and there you can edit the world seed, turn monsters off, change or add a static IP address, etc.
To change games modes in Minecraft Pocket Edition, go to edit world and tap survival or creative
You have to install WorldEdit with it. It usually comes with the download. Put the WorldEdit.jar in the bin folder.